West System brand epoxy is my personal favorite.  I use it on all projects big and small.  It is fairly thin (low viscosity) so it works really well when applying fiberglass cloth.  In other applications, such as fin fillets, I thicken it using one of the many different types of fillers also offered by West System.

I like the #406 Colloidal Silica filler the best as an all around general purpose filler.  It is light weight, very strong and makes a nice smooth creamy mixture that is very easy to work with.  It can be used to prevent the epoxy from running in vertical joints.

For fiber glassing body tubes I prefer the "slow" (206) hardener so that I have plenty of time to get the job done without rushing.  Consequently, I just end up using the 206 hardener for everything else too!  For information about pot life and curing time for various hardeners see the West System guide book.

I buy the #105 epoxy resin in the gallon size. 

Since the mix ratio is 5:1 the #206 hardener comes in a quart can that is not quite full.

Loctite Hysol E-20HP is a high strength industrial adhesive with high sheer strength and resistance to peeling. It can be purchased at McMaster-Carr (part number 6430A19) for about $9.72 for a 50ml cartridge.  An applicator gun (part number 74695A71) and a mixing nozzle (part number 74695A12) are also needed.  The gun uses a ratchet scheme to push a plunger into the cartridge.  The plunger pushes out the correct 2:1 ratio of resin and hardener.  The mixing nozzle is a long plastic tube with a spiral type internal construction that causes the two streams of liquid to intermix before exiting out the tip.  There is no measuring and no hand mixing necessary.  The 2:1 mix ratio is always correct.  The nozzle also makes it extremely easy to apply the epoxy exactly where it is needed.   All of this speeds up the work and cuts down on wasted epoxy.  This system is very handy and a real pleasure to use!  The gun is about $23 and the mixing nozzles are about $0.75 each.  The mixing nozzle mounts onto the front of the cartridge with a type of bayonet scheme. It can be easily removed and is disposable. Once removed, the cap can be replaced onto the front of the cartridge.  It too uses a bayonet mount scheme.  I have not tried to clean out any mixing nozzles after use.  It might not be possible.  I just use a new one each session. 

If you only need a very small amount of epoxy, it is also very easy to dispense it without a mixing nozzle.  Just remove the cap from the cartridge and squirt some of the epoxy onto a small 3x5 card and then stir the mixture with a small stick.  This avoids consuming a mixing nozzle when you only need a small amount of epoxy.  It also avoids wasting the amount of epoxy that gets left inside the mixing nozzle. However, for bigger jobs the mixing nozzle is well worth it and very handy.